Polymers composed of 2% by weight or more of a structural unit represented by the following structural formula (I) ##STR2## (wherein R is a hydrogen atom, an alkyl group, an aryl group or an alicyclic group of 1 to 20 carbon atoms) and 98% by weight or less of an eithylenic monomer unit, characteristically are thermoplastic and have excellent heat resistance.
However, because these polymer have insufficient surface adhesion resistance, molded articles produced therefrom are affected by contacts, impacts, scratching, etc. given by other objects during their transportation, handling or use an consequently receive damages at the surface or give reduced product yields or have deteriorated appearances.
Various methods for improving the inherent drawbacks of these synthetic resin molded articles have been investigated. Such methods include, for example, a method wherein the surface of a synthetic molded article is coated with a polyfunctional acrylate or methacrylate monomer as a crosslinking-curable coating material, having two or more polymerizable, ethylenically unsaturated groups in one molecule and the resulting coated molded article is exposed to active energy rays to form a crosslinking-cured film on the surface of the synthetic resin molded article by radical polymerization.
Such polyfunctional (meth)acrylate monomer [(meth)acrylate implies acrylate or methacrylate and this definition is applied also hereinunder] have an excellent polymerization activity when exposed to active energy rays. Therefore, these monomers are proposed as a material for quick-drying inks in U.S. Pat. Nos. 3,661,614, 3,551,311 and 3,551,246, UK Pat. No. 1,198,259, etc. Further, the application of these polyfunctional (meth)acrylate monomers as a surface improver for synthetic resin molded articles is proposed in U.S. Pat. Nos. 3,552,986, 2,413,973 and 3,770,490, etc.
Meanwhile, the present inventors too previously found that multifunctional (meth)acrylate monomers are excellent in polymerizability by crosslinking-curing when exposed to active energy rays and are an effective material for formation of a crosslinking-cured film capable of improving the surface wear resistance of synthetic resin molded articles, and have made various proposals (in, for example, Japanese Patent Publication Nos. 42,211/1973, 12,886/1974, etc.).
However, these materials for forming a crosslinking-cured film are applied in most cases only to general-purpose base materials, and a plastic base material giving a crosslinking-cured film having good adhesiveness is insufficient in heat resistance and a plastic base material having good heat resistance is insufficient in adhesiveness between plastic base materials and the crosslinking-cured film.